A First Glance at “The First”
In order to have the AMRAD 136.750 kHz beacon on the air as soon as possible, the Board of Directors of AMRAD decided to purchase a “The First”, a commercially-made LF transmitter. The unit, manufactured in Holland by Ropex, was purchased through Nevada, their British distributor. Somehow, I inherited the job of putting the unit on frequency, and testing it prior to deploying it as our beacon. What follows is my own opinion of the unit, after having had it on my bench for about two weeks.
As I write this review, this sturdy little unit has been generating 30 watts of RF (110 volts peak-to-peak) into my 50-ohm test load for several hours now. It draws 3.25 amperes from my 13.8 V dc regulated power supply, hence an overall efficiency approaching 69%.
“The First” is a compact, fan-cooled LF transmitter capable of outputting either 30 or 130 watts of RF. It comes pre-crystalled on 136.533 kHz. The supplied operating instructions are simple, if somewhat succinct. The output stage operates in class D and incorporates a overcurrent protection circuit.
The first problem I encountered was to change the unit’s frequency of operation, I would have to unsolder the crystal, This is something I believe to be unacceptable for two reasons: First, as European LF amateur operators have discovered, there is so much interference in the 136 kHz band that the ability to select a good spot within that band is important. And that spot will almost certainly not be 136.533! Second, for a unit in that price-range (£170 or approximately $260) I would have expected that the crystal would be socketed anyway. The next problem had to do with the actual removal of the crystal. This requires (a) opening the enclosure, (b) extracting the printed circuit board from the enclosure, and (c) separating the printed board from its heat sink, three definitely non-trivial operations.
As I examined the unit now laying all over my bench, I found a printed-circuit board that appeared to be of very good quality, well laid-out, populated with quality components, and bolted to a thick piece of aluminum as a heat-sink. What struck me is that it is as if two separate design teams had been asked to work on “The First.” One team would have worked on the electronic portion consisting of the printed circuit board and its heat sink; it appears well designed, and operates as advertised. Then, somehow, someone else must have been brought in and asked to place that RF unit in a box. That second team (assuming my hunch is correct) would probably benefit from taking an introductory course in industrial design. The enclosure selected for the job is a poor choice, difficult to open and to put back together, with the panel-mounted components poorly fixed, and the wires linking those components to the printed-circuit board barely long enough. Several ground connections on the panel are made by soldering the wires directly to a threaded part, insuring that this particular component can never be removed, repaired or changed in the future, except with some major surgery.
WHAT I LIKED
The unit operates as advertised. Although I haven’t had yet an opportunity to connect the unit to a spectrum-analyzer, spectral purity as displayed on my oscilloscope appears excellent, thanks to several large inductors in the output circuit.
WHAT I DID NOT LIKE
The mechanical construction of the unit, the lack of schematics, and the fact that one of the ICs had its markings purposely erased. Also I found inadmissible that the crystal is soldered in place, and that no provision exists to drive the unit from a VFO.
Let us hope that the “Mark II” version of the unit will benefit from some serious mechanical redesign.
André Kesteloot, N4ICK.